•The Nature of Liquids

Liquids

• The ability of gases and liquids to flow allows then to conform to the shape of their containers.

• Liquids are much more dense then gases.

More on liquids….

»Increasing the pressure on a liquid has hardly any effect on its volume. (The same is true of solids).

»For that reason, liquids and solids are known as condensed states of matter.

Key Concept!!!

• The interplay between the disruptive motions of particles in a liquid and the attractions among the particles determines the physical properties of liquids.

Evaporation & Vaporization• The conversion of a liquid to a gas or

vapor is called vaporization.

• When such a conversion occurs at the surface of a liquid that is not boiling, the process is called evaporation.

Key Concept • During evaporation, only those

surface molecules with a certain minimum kinetic energy can escape from the surface of the liquid.

More on Evaporation….

• Liquid evaporates faster when heated. This is because heating a liquid increases the average kinetic energy of its particles.

• As evaporation occurs, the particles with the highest kinetic energy escape first.

• Evaporation is a cooling process!!

Vapor Pressure

Vapor (Gas)Liquid

evaporation

Condensation

• An increase in temperature of a contained liquid increases the vapor pressure.

Boiling Pointvapor pressure = external pressure

• When a liquid is heated to a temperature at which particles throughout the liquid have enough kinetic energy to vaporize, the liquid begins to boil.

• Because atmospheric pressure is lower at higher altitudes, boiling points decrease at higher altitudes.

• Although vapor has the same kinetic energy as the liquid, its potential (or stored energy) is much higher.

»Thus a burn from steam is more severe than one from an equal mass of boiling water at the same temperature.

The Nature of Solids

• The general properties of solids reflect the orderly arrangement of their particles and the fixed locations of their particles.

Melting Point

Solid Liquid

Melting

Freezing

Crystal Structure

• The type of bonding that exists between particles in crystals determines their melting points.

» Not all solids melt however. » Wood and cane sugar for example,

decompose when heated.

• Allotropes are two or more different molecular forms of the same element in the same physical state.

Graphite

DiamondFullerene

Allotropes of Carbon

• Amorphous Solids lack an ordered internal structure.

»Rubber, plastic and asphalt are examples

Changes of State

• Sublimation is the change of a substance to a vapor without passing through the liquid state.

Phase Diagrams

• A phase diagram gives the conditions of temperature and pressure at which a substance exists as a solid, liquid and gas (vapor).

Phase Diagram Cont…

• The Triple Point describes the only set of conditions at which all three phases can exist in equilibrium with one another.

• A decrease in pressure lowers the boiling point and raises the melting point

• An increase in pressure will raise the boiling point and lower the melting point.